Steven Moffat, lead writer of the BBC show, says Doctor Who could one day be a
woman - but not for reasons of 'political correctness'

Political correctness must not be allowed to turn the next Doctor Who into a woman, Steven Moffat has said.

Doctor Who could be played by a woman only for "aesthetic" reasons, according to Steven Moffat, who said he would resist all "political" efforts to cast a female Time Lord.

Moffat, lead writer and executive producer on the programme, said an actress could be cast only if the perfect candidate popped into his head. "When that person is a woman, that's the day it will happen," he said.

With each successive casting change, the clamour for a female Doctor grows louder. Olivia Colman was linked to the role last year, and Dame Helen Mirren said it was "well over time to have a female Doctor". The job went to Peter Capaldi.

Moffat succeeded Russell T Davies as the BBC show's lead writer and executive producer in 2009.

During a Q&A session at the Hay Festival, the question of whether he would ever consider a female Doctor Who raised the biggest applause of the night.

He replied: "I don't know why I'm the one who gets the grief for this. I'm the one who put the dialogue into the show to say it can happen.

"Do you know how it will happen? It will not happen that somebody sits down and says we must turn the Doctor into a woman. That is not how you cast the Doctor.

"A person will pop into the showrunner's head and they'll think. 'Oh, my God, what if it was that person?' And when that person is a woman, that's the day it will happen.

"Casting is the dark arts of television. It is everything. That decision is central and absolute to everything you do. It's the difference between a television programme and a sensation.

"So you don't mess around with that; you don't cast for any other reason than for passion and for aesthetics. It's not a political decision, it's an aesthetic decision and will always be."

Capaldi was chosen in just such a manner. Moffat explained: "Peter Capaldi just kept popping into my head. I got him round to my house to audition. And He didn't know he was the only person auditioning."

Asked why he had gone for an older Doctor - Capaldi is 56 - Moffat replied: "Can you imagine if we had cast another handsome yet quirky young man with entertaining hair? The show would just have become that little bit more ordinary. You start to work out what the joke is and it's never quite as magic again."

Moffat was also asked if he would consider making the Doctor's companion something other than a "20th century female". He disclosed: "I would consider that. I very nearly did it last time."

He also disclosed that the BBC had considered pulling the plug on Doctor Who after David Tennant left, fearing that nobody else could fill his shoes.

"David owned that role in a spectacular way, gave it an all-new cheeky sexy performance and became a national treasure. And he didn't do it instantly, he did it over time. So the idea that Doctor Who could go on at all in the absence of David was a huge question," Moffat said.

"I didn't realise how many people thought it wouldn't succeed at all. That was quite terrifying when I found out about it later.

I think there were plans maybe to consider ending it. It was Russell saying, you are not allowed to end it."

Efforts to change the Daleks have also been resisted. Moffat laughed: "There's a sink plunger sticking out of a Dalek. And occasionally people, including myself, have thought should we get rid of what is very obviously something you stick down the lav.

"What does it do? Nobody knows. Why don't they have two guns? They're capable of two things - killing people and sink plunging. But you can't get rid of them because it would be wrong and awful and heretical."